Frequency hopping signal generation system and method

Abstract

The invention discloses a frequency hopping signal generation system and method, and belongs to the technical field of microwave photons. The system comprises an optical frequency comb module, a signal processing module and a photoelectric conversion module, wherein the optical frequency comb module generates an optical frequency comb as a system frequency hopping carrier and a local oscillator through a cascade external modulator; the signal processing module carries out channelization processing on the optical frequency comb to respectively obtain a carrier channel and a local oscillation channel, the carrier channel loads an input electric frequency hopping signal to a carrier, and the local oscillation channel is input into the high-speed optical switch for path selection; combining the modulated carrier channel and the selected local oscillator channel, inputting the combined channel into the photoelectric conversion module, adjusting the bandwidth of an electric frequency hopping signal to enable the electric frequency hopping signal to be equal to the comb tooth interval of the optical frequency comb, and outputting the frequency hopping signal; compared with an electronics frequency hopping scheme and other photonics frequency hopping schemes, the frequency hopping signal bandwidth and the frequency band number generated by the method are greatly improved, and the anti-interference performance of frequency hopping communication is greatly improved.

Description

Technical Field

[0001] The present invention relates to a frequency hopping signal generating system and method, belonging to the technical field of microwave photons. Background Art

[0002] Unlike traditional fixed-frequency signals, frequency-hopping signals, whose carrier frequency varies dynamically over time, have crucial applications in wireless communications and radar systems. In wireless communications, frequency-hopping signals can significantly improve the system's anti-interference and anti-interception capabilities. Even if a frequency or frequency band is interfered with, frequency-hopping communications can circumvent it, bypassing the interfering frequency band and ensuring normal information transmission. In radar systems, frequency-hopping signals can significantly increase the time-domain bandwidth product, enabling high-precision detection over a wide range.

[0003] Currently, frequency-hopping signals are primarily generated electronically using electronic components, and the technology is relatively mature. However, due to the "electronic bottleneck" of electronic devices, frequency, bandwidth, and rate are limited. As a result, the bandwidth of these electronically generated frequency-hopping signals is limited to a few GHz, and the hopping rate is limited to the kHz level. With the ever-increasing bandwidth and quality requirements for wireless communications, as well as the increasing detection accuracy and range requirements for radar systems, traditional frequency-hopping signal generation methods are no longer able to meet current needs.

[0004] In recent years, the continuous development of microwave photonics technology has made it possible to generate high-speed, wide-bandwidth frequency-hopping signals. Microwave photonics, with its advantages of high operating frequency, large instantaneous bandwidth, and reconfigurability, can effectively address the challenges faced by electrical-domain frequency-hopping systems. Consequently, numerous scholars at home and abroad have conducted in-depth research and proposed numerous microwave photonics-based frequency-hopping signal generation schemes.

[0005] However, current microwave photonic frequency-hopping signal generation methods have several limitations and shortcomings. First, the operating frequency range of reported frequency-hopping signals is mostly limited to below 25 GHz, and there are few reports on frequency-hopping signal generation technologies for the high-frequency band (EHF). Second, while frequency-hopping schemes based on photonic switches have a frequency-hopping bandwidth of tens of GHz, most schemes have significantly fewer frequency points than electronic frequency-hopping methods, often with only two. This makes it difficult to simultaneously achieve a large frequency-hopping bandwidth and a large number of frequency points, making it difficult to meet the frequency channel requirements of high-frequency millimeter-wave communication systems. Summary of the Invention

[0006] The present invention aims to overcome the shortcomings of the prior art and provide a frequency hopping signal generation system and method. By using a single optical frequency comb as the system local oscillator source, combined with a wavelength selective switch to achieve channelization, and adding a high-speed optical switch to select the channel, the frequency hopping signal generation is finally achieved through heterodyning.

[0007] To achieve the above object / to solve the above technical problems, the present invention is implemented by the following technical solutions:

[0008] In the first aspect: A frequency hopping signal generation system includes an optical frequency comb module, a signal processing module, and an optoelectronic conversion module. The optical frequency comb module generates an optical frequency comb as the system frequency hopping carrier and local oscillator through cascaded external modulators.

[0009] The signal processing module performs channelization processing on the optical frequency comb to obtain a carrier channel and a local oscillator channel respectively. The carrier channel loads the input electrical frequency hopping signal onto the carrier, and the local oscillator channel inputs a high-speed optical switch for path selection.

[0010] After combining the modulated carrier channel and the selected local oscillator channel, the combined signal is input into the optoelectronic conversion module. By adjusting the bandwidth of the electrical frequency hopping signal to be equal to the comb tooth interval of the optical frequency comb, a frequency hopping signal without blind spots is output.

[0011] Optionally, the optical frequency comb module includes a continuous light laser, a cascaded external modulator, a microwave source, an electrical amplifier, and a DC power supply. The light generated by the continuous light laser is input into the cascaded external modulator. The DC power supply is input into the bias voltage port of the cascaded external modulator, and the microwave source is input into the RF input port of the cascaded external modulator. The electrical amplifier is arranged on the circuit between the microwave source and the cascaded external modulator.

[0012] Optionally, the cascaded external modulator includes a first-stage modulator and a second-stage modulator. The DC power supply and the microwave source are respectively connected to the first-stage modulator and the second-stage modulator. The first-stage modulator is connected to a first electrical amplifier, and the second-stage modulator is connected to a second electrical amplifier.

[0013] Optionally, the signal processing module includes a wavelength selection switch, a high-speed optical switch, and a dual-parallel Mach-Zehnder modulator. The wavelength selection switch receives the optical frequency comb input from the optical frequency comb module and performs channelization processing on the optical frequency comb to obtain a carrier channel and a local oscillator channel respectively. The dual-parallel Mach-Zehnder modulator is used to load the electrical frequency hopping signal onto the carrier, and the high-speed optical switch is used to select the local oscillator channel.

[0014] Optionally, the optoelectronic conversion module includes a coupler, an optical amplifier, and a photodetector. The coupler is used to combine the carrier channel after loading the signal and the selected local oscillator channel and input the combined signal into the optoelectronic conversion module. After power compensation by the optical amplifier, the combined signal is input into the photodetector for optoelectronic conversion to obtain a frequency hopping signal.

[0015] In the second aspect: A method for generating a frequency hopping signal, the method includes: The optical frequency comb module outputs a light source from the continuous light laser to the cascaded modulator, where the cascaded modulator includes a first-stage modulator and a second-stage modulator; The cascaded modulator receives the light source signal, and inputs the upper and lower arms of the cascaded modulator through the radio frequency drive signal and the DC bias signal, and outputs an optical frequency comb; The optical frequency comb is input into the signal processing module for channelization processing, separated into a carrier channel and multiple local oscillator channels, and multiple local oscillator channels are selected to obtain a local oscillator signal; An electrical frequency hopping signal is loaded onto the carrier channel to obtain a modulated signal; The local oscillator signal of the selected local oscillator channel and the modulated signal are combined and then input into the optoelectronic conversion module. After power compensation by the optical amplifier, it is injected into the photodetector for heterodyne beating to obtain a frequency hopping signal without blind spots.

[0016] Optionally, the expression of the output light source of the continuous light laser is:

[0017] , wherein, is the amplitude of the input optical signal, is the continuous optical angular frequency, is the exponential function, is the imaginary number.

[0018] Optionally, the radio frequency drive signal is emitted by a microwave source, and its expression is: , wherein, is the input radio frequency angular frequency, is the signal amplitude, is the initial phase, then the expression of the output signal of the first-stage modulator is: , and are the phases generated by the DC power supply in the upper and lower arms of the first-stage modulator, is the gain generated by the electrical amplifier. By adjusting the voltage magnitude input by the DC power supply, the phases generated by the DC biases of the upper and lower arms are made to satisfy , and the output signal is simplified to: ,

[0019] wherein, is an integer, represents the mth-order Bessel function, is the half-wave voltage of the first-stage modulator. The first-stage modulator outputs multiple sidebands. By adjusting the electrical amplifier, the amplitudes of the radio frequency drive signals input to the upper and lower arms of the first-stage modulator are made to satisfy , and the output signal of the first-stage modulator generates an optical frequency comb, and the comb tooth spacing is .

[0020] Optionally, the second-stage modulator broadens the optical frequency comb generated by the first-stage modulator. The connection relationship between the second-stage modulator and the microwave source and the DC power supply, as well as the input signal magnitude, are the same as those of the first-stage modulator. The generated optical frequency comb is expressed as: , wherein, is an integer, representing the position of the comb tooth relative to the center frequency, represents the number of available comb teeth on both sides of the center frequency, represents the amplitude of the th comb tooth of the optical frequency comb, represents the phase of the th comb tooth of the optical frequency comb, represents the th comb tooth frequency, can be further expressed as: .

[0021] Optionally, the carrier channel after loading the signal and the selected local oscillator channel are expressed as: , , wherein, is the amplitude of the carrier channel after modulation, is the phase of the carrier channel after modulation; is the carrier channel frequency, is the local oscillator channel frequency, is the starting position of the local oscillator channel, is the number of local oscillator channels; The carrier channel after loading the signal and the selected local oscillator channel are combined and then input into the optoelectronic conversion module. The combined signal is: , wherein, is the gain multiple of the optical amplifier. The combined signal is input into the photodetector for optoelectronic conversion to obtain the frequency hopping signal: , wherein, is the current responsivity of the PD, is the DC component.

[0022] Compared with the prior art, the beneficial effects achieved by the present invention: 1. The method of the present invention realizes the generation of ultra-wideband frequency-hopping signals by taking advantage of the large bandwidth, reconfigurability, and ultra-high speed of photonics. The frequency can reach above terahertz, and the bandwidth exceeds 50 GHz. Compared with the electronic frequency-hopping scheme and other photonics frequency-hopping schemes, the bandwidth and the number of frequency bands of the frequency-hopping signals generated by this method have been greatly improved, significantly enhancing the anti-jamming performance of frequency-hopping communication and the detection accuracy of radar.

[0023] 2. The core of the present invention is optoelectronic combined frequency hopping. That is, when the bandwidth of the electrical frequency-hopping signal is equal to the spacing between the teeth of the optical frequency comb, the frequency-hopping signals generated by this system can achieve full coverage within the working frequency band, realizing frequency hopping without blind spots, and greatly enhancing the anti-jamming ability of the system.

[0024] 3. Compared with dual optical frequency combs and other microwave photonics frequency-hopping signal generation methods, this method can achieve comparable performance only by using a single optical frequency comb. It has the advantages of simplicity, flexibility, and compact structure, and can generate ultra-wideband and multi-frequency point frequency-hopping signals with relatively low power consumption and device volume.

[0025] 4. Thanks to the wideband modulation range of the modulator and the fast switching characteristics of the optical switch, the frequency-hopping signals generated by this method have the characteristics of wideband and fast switching, and the frequency-hopping speed can reach 100 ns.

[0026] 5. The present invention has the characteristics of flexibility and reconfigurability. By changing the driving signal for generating the optical frequency comb, the frequency-hopping channels of the system can be reconfigured. Moreover, by increasing the spectral width of the optical frequency comb, frequency-hopping signals with higher frequency bands and larger bandwidths can be generated. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is the system diagram provided by the embodiment of the frequency-hopping signal generation system of the present invention;

[0028] Figure 2 is the schematic diagram of optoelectronic combined frequency hopping of the present invention;

[0029] Figure 3 is the optical frequency comb spectrogram of the present invention;

[0030] Figure 4 is the spectrogram of single-tone signal down-converted carrier-suppressed single-sideband modulation of the present invention;

[0031] Figure 5 is the frequency-hopping channel spectrogram and flatness curve of the present invention

[0032] Figure 6 is the spectrogram of the frequency-hopping signal without blind spots of the present invention

[0033] Figure 7 is the adjacent channel switching spectrogram of the present invention

[0034] Figure 8It is the channel frequency and the time-frequency diagram of the frequency hopping signal during the different channel switching processes of the present invention.

[0035] In the figure: 1 - continuous light laser; 2 - first-level modulator; 3 - second-level modulator; 4 - microwave source; 5 - first electrical amplifier; 6 - second electrical amplifier; 7 - DC power supply; 8 - wavelength selection switch; 9 - high-speed optical switch; 10 - dual-parallel Mach-Zehnder modulator; 11 - electrical frequency hopping signal; 12 - coupler; 13 - optical amplifier; 14 - photodetector. Specific embodiments

[0036] In order to make the technical means, creative features, achieved purposes and functions of the present invention easy to understand, the present invention will be further described below in conjunction with specific embodiments.

[0037] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation to the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first", "second", etc. may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise specified, the meaning of "plurality" is two or more.

[0038] In the description of the present invention, it should be noted that unless otherwise clearly specified and limited, the terms "installed", "connected", "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood through specific situations.

[0039] Embodiment 1, as Figure 1 shown, a frequency hopping signal generation system includes three parts: an optical frequency comb module, a signal processing module, and a photoelectric conversion module; Among them, the optical frequency comb module includes a continuous light laser 1, a first-stage modulator 2, a second-stage modulator 3, a microwave source 4, a first electrical amplifier 5, a second electrical amplifier 6, and a DC power supply 7; the signal processing module includes a wavelength selection switch 8, a high-speed optical switch 9, a dual-parallel Mach-Zehnder modulator 10, and an electrical frequency hopping signal 11; The optoelectronic conversion module includes a coupler 12, an optical amplifier 13, and a photodetector 14; the signal processing module performs channelization processing on the optical frequency comb to respectively obtain a carrier channel and a local oscillator channel. The carrier channel loads the input electrical frequency hopping signal onto the carrier, and the local oscillator channel inputs the high-speed optical switch for path selection, as Figure 2 shown; After combining the modulated carrier channel and the selected local oscillator channel and inputting them into the optoelectronic conversion module, by adjusting the bandwidth of the electrical frequency hopping signal to be equal to the tooth pitch of the optical frequency comb, a frequency hopping signal without blind spots is output.

[0040] The light generated by the continuous light laser is input to the cascaded external modulator. The DC power supply inputs the bias voltage port of the cascaded external modulator, and the microwave source inputs the RF input port of the cascaded external modulator. The electrical amplifier is arranged on the circuit between the microwave source and the cascaded external modulator.

[0041] Among them, the carrier channel and the local oscillator channel respectively come from different teeth of the optical frequency comb generated by the same laser, have good coherence, and can effectively improve the quality of the frequency hopping signal.

[0042] As Figure 1 shown, the bandwidth of the input electrical frequency hopping signal 11 is equal to the tooth pitch of the optical frequency comb, so as to ensure that the generated frequency hopping signal completely covers the working bandwidth and realizes frequency hopping without blind spots.

[0043] An optical frequency comb is generated through the first-stage modulator 2 and the second-stage modulator 3. By adjusting the input drive signal power and the DC signal voltage, the unevenness generated by the first-stage and second-stage modulators cancels each other out, and an ultra-flat wide-spectrum optical frequency comb can be generated, which is used as the carrier channel and the local oscillator channel of the system.

[0044] The channel interval of the wavelength selection switch is equal to the tooth pitch of the optical frequency comb, so as to separate the optical frequency comb into multiple parallel channels. By selecting different channels as the carrier channel and the local oscillator channel and combining with the fast switching of the high-speed optical switch, the generation of the frequency hopping signal is realized.

[0045] The present invention proposes a frequency hopping signal generation system. By using a single optical frequency comb as the system local oscillator source, channelization is realized in combination with a wavelength selection switch, the channels are selected by a high-speed optical switch, and finally the generation of the frequency hopping signal is realized by the heterodyne method. The core idea of this method is the optoelectronic combination, that is, the combination of optical-domain multi-band frequency hopping and electrical-domain fine frequency hopping, which can generate ultra-wideband, multi-frequency point, and frequency hopping signals without blind spots.

[0046] The control of the frequency hopping sequence can be achieved by controlling the signal through the high-speed optical switch 9. When the electrical frequency hopping signal is equal to the optical frequency comb spacing, full coverage within the operating frequency band can be achieved, that is, frequency hopping without blind spots.

[0047] Embodiment 2 discloses a method for generating a frequency hopping signal, and the method includes: Step 1, the optical frequency comb module outputs a light source to the cascade modulator through a continuous light laser, where the cascade modulator includes a first-stage modulator and a second-stage modulator; Step 2, the cascade modulator receives the light source signal, and inputs the radio frequency drive signal and the DC bias signal into the upper and lower arms of the cascade modulator, and outputs an optical frequency comb; Step 3, input the optical frequency comb into the signal processing module for channelization processing, separate it into a carrier channel and multiple local oscillator channels, and select multiple local oscillator channels to obtain a local oscillator signal; Step 4, load an electrical frequency hopping signal on the carrier channel to obtain a modulated signal; Step 5, combine the local oscillator signal of the selected local oscillator channel with the modulated signal and input it into the optoelectronic conversion module. After power compensation by the optical amplifier, it is injected into the photodetector for heterodyne beating to obtain a frequency hopping signal without blind spots.

[0048] For the above method, in this embodiment, it is further elaborated that in the optical frequency comb module, the laser generated by the continuous light laser 1 has a frequency of , and is used as the seed light source of the system optical frequency comb. The optical signal output by the continuous light laser 1 is injected into the first-stage cascade modulator 2 and the second-stage cascade modulator 3. The radio frequency drive signals output by the microwave source 4 are respectively input into the upper and lower arms of the first-stage modulator 2 and the second-stage modulator 3. By tuning the first electrical amplifier 5 and the second electrical amplifier 6 and the DC power supply 7, it is ensured that the amplitude difference of the drive radio frequency signals of the upper and lower arms of the first-stage modulator 2 and the second-stage modulator 3 satisfies , and the phase difference satisfies , and then the optical frequency comb can be output. The tooth spacing of the optical frequency comb is controlled by the microwave source 4 and is .

[0049] The optical frequency comb input signal processing module performs channelization processing through the wavelength selection switch 8, and separates it into a carrier channel and multiple local oscillator channels. The channel interval of the wavelength selection switch 8 corresponds to the tooth spacing of the optical frequency comb.

[0050] Multiple local oscillator channels are input into the high-speed optical switch 9 in parallel for channel selection. The position of the local oscillator channel output by the optical switch 9 is determined by the control signal.

[0051] The carrier tooth is input into the dual-parallel Mach-Zehnder modulator 10 for signal loading, and the modulation format is carrier-suppressed single-sideband modulation, and the loading signal is the electrical frequency hopping signal 11.

[0052] After the carrier comb teeth after signal loading and the selected local oscillator comb teeth are combined through coupler 12, they are input into the optoelectronic conversion module. First, power compensation is performed by optical amplifier 13, and then it is injected into photodetector 14 for heterodyne beating to obtain a frequency hopping signal, whose frequency expression is: .

[0053] In the optical frequency comb module, the output light source expression of continuous wave laser (1) is: , wherein, is the amplitude of the input optical signal, is the continuous wave angular frequency, is the exponential function, is the imaginary number. Then, the output optical signal of continuous wave laser 1 is injected into first-stage modulator 2. Among them, the expression of the radio frequency drive signal output by microwave source 4 is: ; wherein, is the input radio frequency angular frequency, is the signal amplitude, is the initial phase. Then the expression of the signal output by first-stage modulator 2 is: , and are the phases generated by DC power supply 7 on the upper arm and the lower arm of first-stage modulator 2. is the gain generated by the first electrical amplifier (5). By adjusting and DC power supply 7, the phases generated by the DC biases of the upper and lower arms are made to satisfy . At this time, the signal output by first-stage modulator 2 can be simplified to: , wherein, is an integer, represents the m-th order Bessel function, is the half-wave voltage of first-stage modulator 2. It can be seen from the expression that first-stage modulator 2 outputs multiple sidebands. Then, by adjusting the first electrical amplifier 5, the amplitudes of the radio frequency drive signals input to the upper and lower arms of first-stage modulator 2 are made to satisfy . At this time, the amplitudes of the sidebands of the signal output by first-stage modulator 2 are not very different, that is, an optical frequency comb is generated, and the comb tooth spacing is .

[0054] Similarly, the configuration method of the secondary modulator 3 is the same as that of the primary modulator 2. The gain of the second electrical amplifier 6 is equal to that of the first electrical amplifier 5. The RF drive signals and DC biases input into the two amplifiers from the microwave source 4 and the DC power supply 7 are consistent. In this system, the main function of the secondary modulator 3 is to broaden the optical frequency comb generated by the primary modulator 2 and improve its flatness simultaneously. Then, the finally generated optical frequency comb can be expressed as: , wherein, is an integer, representing the position of the comb tooth relative to the center frequency, represents the number of available comb teeth on both sides of the center frequency. and respectively represent the amplitude and phase of the th comb tooth of the optical frequency comb, represents the th comb tooth frequency. can be further expressed as: ; Then, the optical frequency comb output by the secondary modulator 3 enters the signal processing module. First, the optical frequency comb is separated into parallel channels by the wavelength selection switch 8, and the channel spacing of the wavelength selection switch is equal to the comb tooth spacing of the optical frequency comb. Among them, a suitable channel is selected as the carrier channel, and the other channels are used as the local oscillator channels. Here, it is assumed that the frequency of the carrier channel is , and the frequency of the local oscillator channel is , is the starting position of the local oscillator channel, is the number of local oscillator channels.

[0055] Then, the carrier channel is input into the dual-parallel Mach-Zehnder modulator 10 for signal loading. The modulation format is carrier-suppressed single-sideband modulation, and the input signal is the electrical frequency-hopping signal 11 with a bandwidth of . The local oscillator channels are input into the high-speed optical switch 9 in parallel for channel selection. The optical switch makes a selection according to the control signal and outputs one local oscillator channel. The output channel of the optical switch can be controlled by the control signal. Then, the carrier channel after signal loading and the selected local oscillator channel can be expressed as: , , wherein, and are the amplitude and phase of the carrier channel after modulation. Then, the carrier channel after signal loading and the selected local oscillator channel are combined by the coupler 12 and then input into the optoelectronic conversion module, and power compensation is performed by the optical amplifier 13. The combined signal is: ; wherein, is the gain multiple of the optical amplifier 13. Finally, the combined signal is input into the photodetector 14 for photoelectric conversion to obtain a frequency-hopping signal: ; wherein, is the current responsivity of the PD, is the DC component.

[0056] Embodiment 3. In this embodiment, a simulation platform is built using Optisystem 15.0 software for verification. In this system, the OFC is generated by cascading a dual-port Mach-Zehnder modulator. The input radio frequency signal has a frequency of 5 GHz and an amplitude of 1V. By adjusting the gain of the upper-arm electrical amplifier in the dual-port Mach-Zehnder modulator, the amplitude difference between the upper and lower-arm radio frequency drive signals is made to satisfy ( = 4V is the half-wave voltage of the modulator), and the phase difference satisfies , then a flat optical frequency comb can be generated, as shown in Figure 3 . It can be seen from the simulation results that the tooth spacing of the optical frequency comb generated by this method is 5 GHz, the tooth profile of the optical frequency comb is clearly distinguishable, the spectral flatness is good, and the number of teeth in the 3 dB fluctuation bandwidth is stable at more than 20. Moreover, the quality of the OFC generated by this method is good, and the carrier-to-noise ratio is better than 50 dB. Here, the present invention uses the right-side teeth shown in Figure 3 as the signal teeth to load the frequency-hopping signal, and the 12 teeth on the left side are used as the local oscillator to form 12 frequency-hopping channels.

[0057] Next, the optical frequency comb is input into an optical demultiplexer to be separated into 12 parallel frequency-hopping local oscillator channels and 1 signal channel. Among them, the signal channel is output separately, and the 12 frequency-hopping local oscillator channels are input into an optical switch array, and channel selection is performed according to the optical switch control signal. In the signal channel, the electrical frequency-hopping signal is loaded through an IQ modulator, and the modulation format is carrier-suppressed single-sideband modulation. Finally, after the local oscillator channel and the signal channel are combined, they are input into an erbium-doped fiber amplifier for amplification to compensate for the power loss, and then injected into a photodetector for photoelectric conversion to obtain a frequency-hopping signal.

[0058] First, this embodiment tests the carrier-suppressed single-sideband modulation effect of the IQ modulator. Set the input radio frequency signal as a 2.5 GHz single-tone signal with an amplitude of 1V, and the spectral diagram of the modulated signal channel is as shown in Figure 4As shown. The simulation results show that the carrier-suppressed single-sideband modulation signal generated by this method retains the right +1 order sideband, and the carrier suppression ratio is 35.7 dB, with a relatively high isolation degree. It is worth mentioning that in this system, the carrier-suppressed single-sideband modulation effect is mainly limited by the extinction ratio of the modulator and the IQ phase imbalance. In actual experiments, by using a modulator with a high extinction ratio and a more flat 90-degree phase shifter, the sideband and carrier suppression ratios can be improved, which helps to reduce system spurs.

[0059] Subsequently, this implementation case tested the hopping channel frequency points and working bandwidth of the system without loading signals. The local oscillator channel selected by the optical switch and the signal channel output by the wavelength division multiplexer were directly combined through a coupler and then injected into the photodetector to obtain 12 point-frequency hopping channels without loading signals, as Figure 5 shown. It can be seen from the simulation results that the frequency of the hopping channel is 45 - 100 GHz, the hopping bandwidth is 55 GHz, and the channel interval is 5 GHz. The carrier-to-noise ratio of each hopping channel is greater than 60 dB, and the spurious suppression ratio is greater than 40 dB. Among them, the main reasons for generating spurs are the leakage of signals in other channels in the wavelength division multiplexer and the existence of residual carriers and sidebands in the carrier-suppressed single-sideband modulation process. In addition, due to the difference in the flatness of the optical frequency comb, there is a power difference of about 2.01 dB among the 12 hopping channels, but still maintains good consistency.

[0060] Then, the input signal was set as an intermediate frequency electrical hopping signal of 0 - 5 GHz, the number of frequency points was 8, and the hopping frequency point interval was 625 MHz. It was loaded into the signal channel through the IQ modulator to obtain the spectrum diagram of each hopping channel as Figure 6 shown. It can be seen from the spectrum diagram that when the input hopping signal bandwidth is equal to the hopping channel interval, the hopping signal output by the system is a hopping signal of 45 - 105 GHz, and the bandwidth is 60 GHz. Through this method, the input hopping bandwidth can be expanded to 12 times the original, the hopping frequency points are expanded to 96, and the hopping frequency point interval remains unchanged, realizing continuous working bandwidth, that is, non-blind hopping. This method can combine optical-domain multi-band hopping and electrical-domain fine hopping. While expanding the hopping bandwidth, it realizes continuous ultra-wideband multi-frequency point non-blind hopping, greatly improving the spectrum utilization efficiency and anti-interference ability of the system.

[0061] Subsequently, this embodiment tested the dynamic frequency hopping process of the frequency hopping signal. In this system, the optical switch is a key device for realizing ultra-wideband frequency hopping. The operating frequency band of the frequency hopping signal is directly controlled by the optical switch, and its indicators such as switching speed and crosstalk have a crucial impact on the frequency hopping and de-hopping performance of the system. It is reported that the fastest switching speed of the optical switch can currently reach 100 ns, such as the lithium niobate switch. In this system, in order to ensure that no information is lost during the switching process, the present invention sets the channel switching time of the optical switch to 100 ns, and the residence time of each channel is 1 microsecond.

[0062] When no signal is loaded, this embodiment tested the adjacent channel switching through simulation, and used matlab to draw the time-frequency diagram of the switching process, as Figure 7 shown in (a). It can be seen from the figure that during the process of channel 11 switching to channel 12, the frequency of the frequency hopping channel switches from 95 GHz to 100 GHz, and the switching time is about 105.2 ns, which is consistent with the optical switch setting. In addition, it can be seen that there are weak spurious signals in the time-frequency diagram in addition to the target frequency. This is mainly caused by channel crosstalk and residual sidebands in the demultiplexer and IQ modulator, corresponding to Figure 6 the results.

[0063] Then this embodiment loaded the 0-5 GHz electrical frequency hopping signal into the signal channel and drew the time-frequency diagram of the frequency change of the frequency hopping signal during the process of channel 11 switching to channel 12, as Figure 7 shown in (b). In order to prevent the optical switch switching process from affecting the frequency hopping signal, the channel holding time of the frequency hopping signal should be greater than the channel switching time, or no signal should be transmitted during channel switching. The channel holding time of the input frequency hopping signal is set to 190 ns, and the frequency hopping speed is 10 ns. It can be seen from the simulation results that the channel switching process has no effect on the frequency of the frequency hopping signal.

[0064] Finally, this embodiment tested the switching process of different spaced channels through simulation, and drew the time-frequency diagrams of the frequency hopping signal during the processes of channel 1 to channel 4, channel 1 to channel 8, and channel 1 to channel 12, respectively, as Figure 8 shown. Among them, Figure 8 (a)(b)(c) are the time-frequency diagrams of channel switching when no signal is loaded, and (d)(e)(f) are the time-frequency diagrams after modulating the 0-5 GHz frequency hopping signal. It can be seen from the simulation results that the channel switching times in the three cases are 107.2 ns, 109.3 ns, and 103.7 ns respectively, which are consistent with the optical switch switching time. The simulation results show that the frequency hopping speed of this method is mainly affected by the channel switching speed of the optical switch. The channel switching process will not affect the frequency hopping signal, and the switching speed between different channels is consistent and not affected by the channel frequency interval.

[0065] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A frequency hopping signal generation system, characterized in that, It includes an optical frequency comb module, a signal processing module and an optoelectronic conversion module. The optical frequency comb module generates an optical frequency comb through a cascaded external modulator as the system frequency hopping carrier and local oscillator. The signal processing module performs channelization processing on the optical frequency comb to obtain a carrier channel and a local oscillator channel respectively. The carrier channel loads the input electrical frequency hopping signal onto the carrier, and the local oscillator channel inputs a high-speed optical switch for path selection. The modulated carrier channel and the selected local oscillator channel are combined and then input into the optoelectronic conversion module. By adjusting the bandwidth of the electrical frequency hopping signal to be equal to the tooth spacing of the optical frequency comb, a frequency hopping signal without blind spots is output.

2. The frequency hopping signal generating system according to claim 1, wherein The optical frequency comb module includes a continuous light laser, a cascaded external modulator, a microwave source, an electrical amplifier and a DC power supply. The light generated by the continuous light laser is input to the cascaded external modulator. The DC power supply is input to the bias voltage port of the cascaded external modulator, the microwave source is input to the RF input port of the cascaded external modulator, and the electrical amplifier is arranged on the circuit between the microwave source and the cascaded external modulator.

3. The frequency hopping signal generation system according to claim 2, characterized in that, The cascaded external modulator includes a first-stage modulator and a second-stage modulator. The DC power supply and the microwave source are respectively connected to the first-stage modulator and the second-stage modulator. The first-stage modulator is connected with a first electrical amplifier, and the second-stage modulator is connected with a second electrical amplifier.

4. The frequency hopping signal generation system according to claim 1, characterized in that The signal processing module includes a wavelength selection switch, a high-speed optical switch and a dual-parallel Mach-Zehnder modulator. The wavelength selection switch receives the optical frequency comb input by the optical frequency comb module and performs channelization processing on the optical frequency comb to obtain a carrier channel and a local oscillator channel respectively. The dual-parallel Mach-Zehnder modulator is used to load the electrical frequency hopping signal onto the carrier, and the high-speed optical switch is used to select the local oscillator channel.

5. The frequency hopping signal generating system according to claim 1, characterized in that, The optoelectronic conversion module includes a coupler, an optical amplifier and a photodetector. The coupler is used to combine the carrier channel after loading the signal and the selected local oscillator channel and input them into the optoelectronic conversion module. After power compensation by the optical amplifier, the combined signal is input into the photodetector for optoelectronic conversion to obtain a frequency hopping signal.

6. A method for generating a frequency-hopping signal, characterized in that, The method includes: The optical frequency comb module outputs a light source from the continuous light laser to the cascaded modulator, where the cascaded modulator includes a first-stage modulator and a second-stage modulator. The cascaded modulator receives the light source signal and inputs RF drive signals and DC bias signals to the upper and lower arms of the cascaded modulator to output an optical frequency comb. The optical frequency comb is input to the signal processing module for channelization processing, separated into a carrier channel and multiple local oscillator channels, and multiple local oscillator channels are selected to obtain a local oscillator signal. An electrical frequency hopping signal is loaded onto the carrier channel to obtain a modulated signal. The local oscillator signal of the selected local oscillator channel and the modulated signal are combined and then input into the optoelectronic conversion module. After power compensation by the optical amplifier, they are injected into the photodetector for heterodyne beating to obtain a frequency hopping signal without blind spots.

7. The frequency hopping signal generating method according to claim 6, wherein The expression of the light source output by the continuous light laser is: ， In the formula, is the amplitude of the input optical signal, is the angular frequency of the continuous light, is the exponential function, is the imaginary number.

8. The frequency hopping signal generating method according to claim 6, wherein The radio frequency drive signal is emitted by a microwave source, and its expression is: , Among them, is the input radio frequency angular frequency, is the signal amplitude, is the initial phase, and the expression of the output signal of the first-stage modulator is: , and are the phases generated by the DC power supply in the upper and lower arms of the first-stage modulator, is the gain generated by the electrical amplifier. By adjusting the magnitude of the voltage input to the DC power supply, the phases generated by the DC biases of the upper and lower arms satisfy , and the output signal is simplified to: ， Wherein, is an integer, represents the m-th order Bessel function, is the half-wave voltage of the first-stage modulator. The first-stage modulator outputs multiple sidebands. By adjusting the electrical amplifier, the amplitudes of the RF drive signals input to the upper and lower arms of the first-stage modulator satisfy , and an optical frequency comb is generated by the output signal of the first-stage modulator. The comb tooth spacing is .

9. The frequency hopping signal generating method according to claim 8, wherein The second-stage modulator broadens the optical frequency comb generated by the first-stage modulator (2). The connection relationship between the second-stage modulator and the microwave source and the DC power supply and the magnitude of the input signal are the same as those of the first-stage modulator. The generated optical frequency comb is expressed as: ， wherein, is an integer, representing the position of the comb tooth relative to the center frequency, represents the number of available comb teeth on both sides of the center frequency, represents the th amplitude of the optical frequency comb tooth, represents the th phase of the optical frequency comb tooth, represents the th frequency of the comb tooth, is further expressed as: 。 10. The frequency hopping signal generating method according to claim 6, characterized in that The carrier channel after loading the signal and the selected local oscillator channel are expressed as: ， ， Wherein, is the amplitude of the modulated carrier channel, is the phase of the modulated carrier channel; is the carrier channel frequency, is the local oscillator channel frequency, is the starting position of the local oscillator channel, is the number of local oscillator channels; The carrier channel after loading the signal and the selected local oscillator channel are combined and then input into the optoelectronic conversion module. The combined signal is: ， In the formula, is the gain multiple of the optical amplifier. The combined signal is input into the photodetector for optoelectronic conversion to obtain the frequency-hopping signal: ， Among them, is the current responsivity of PD, is the DC component.

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